C# - Delaying Linq To SQL Select Query Execution

I'm building an ASP.NET MVC site that uses LINQ to SQL. In my search method that has some required and some optional parameters, I want to build a LINQ query while testing for the existence of those optional parameters.

Here's what I'm currently thinking:
using(var db = new DBDataContext())
{
IQueryable<Listing> query = null;
//Handle required parameter
query = db.Listings.Where(l => l.Lat >= form.bounds.extent1.latitude && l.Lat <= form.bounds.extent2.latitude);
//Handle optional parameter
if (numStars != null)
query = query.Where(l => l.Stars == (int)numStars);
//Other parameters...
//Execute query (does this happen here?)
var result = query.ToList();
//Process query...

Will this implementation "bundle" the where clauses and then execute the bundled query? If not, how should I implement this feature?